Merge branch 'context-nav-avatar-bg' into 'master'

Add white background to context header avatar

See merge request !12857

app/assets/stylesheets/new_sidebar.scss

@@ -35,6 +35,7 @@ $new-sidebar-width: 220px;
 
   .avatar-container {
     flex: 0 0 40px;
+    background-color: $white-light;
   }
 
   &:hover {